Neovascularization is critical for the growth for tumors and is important in a variety of angiogenic diseases, such as diabetic retinopathy, arthritis, psoriasis and haemangiomas. More than 70% of cancer patients die from metastatic dissemination of the initial tumor. Tumor neovascularization is the crucial process for survival of a primary tumor and for metastatic dissemination. Angiostatic steroids and heparin with anti-angiogenic agents such as protamin have been used as therapies to suppress tumor growth. These therapeutic approaches have serious limitations, because when the dose of heparin exceeds an optimum level for inhibition of angiogenesis, both tumor growth and angiogenesis are stimulated. Also, high doses of cortisone that are required for antiangiogenesis leads to immunosuppression. Acquisition of an angiogenic phenotype marked a transition from hyperplasia to neoplasia.
Growth factors are substances that induce cell proliferation, typically by binding to specific receptors on cell surfaces. One such growth factor is epidermal growth factor (EGF). EGF induces proliferation of a variety of cells in vivo, and is required for the growth of most cultured cells. EGF is a single-chain polypeptide having a molecular weight of 6 Kd (53 amino acid residues) and three internal disulfide bonds. These three well characterized internal disulfide bonds of the epidermal growth factor peptide define three “loops,” the A, B and C loops. Generally, the A loop is characterized between amino acid residues 1-19, the B loop is characterized between residues 20-31, and the C loop is characterized between residues 34-43. EGF is also known to be a powerful stimulator of cell proliferation. In particular, EGF has been shown to stimulate the growth of epithelial cell tissue in a variety of preparations. Epithelial growth factor receptor (EGFR) plays an important role in epithelial biology and in many human malignancies. EGFR is related to the viral oncogeny, v-erb B, and is overexpressed in many human tumors, including brain, bladder, breast, and squamous cell carcinomas of the head, neck and lung. Thus, EGF-R “activation” is an important regulatory event in stimulating the division of many normal cells as well as in the aberrant growth of some tumor cells. Complete EGF peptides, and antibodies which mimic their action, have been used in such diverse processes as screening for tumoricidal activity and promotion of wound healing. EGFR is a member of the receptor family comprising four, highly homologous proteins, HER2, HER3, and HER4 as well as EGFR. Those proteins in this family consist of an extracellular domain, a transmembrane domain, and an intracellular tyrosine kinase domain. Binding of the ligand such as epithelial growth factor (EGF) activates the intracellular tyrosine kinase domain to induce autophosphorylation of the receptor, which initiates the signaling cascade involved in cell proliferation and survival. EGFR is one of the most suitable targets in cancer therapy.
Lung cancer is the most common malignancy among men and women, and remains the leading cause of cancer-related deaths. Non-small lung carcinoma (NSCLC) accounts for approximately 75-85% of lung cancers. Conventional lung cancer treatments generally show poor clinical response, thus it is of utmost importance to develop novel treatment strategies directed against metastasis. EGFR overexpression occurs in 40-80% of NSCLCs. The EGFR pathway contributes to the pathogenesis and progression of human carcinoma, including cell proliferation, apoptosis, angiogenesis and metastatic spread. Notably, EGFR-directed tyrosine kinase inhibitors (TKIs) such as gefitinib (Iressa, ZD1839), lapatinib (Tykerb, GW572016) and erlotinib (Tarceva, OSI-774) have different sensitivities based on the specific subtypes of NSCLC patients. In addition, gefitinib has been used as a single agent in NSCLC with modest efficacy. However, patients respond differently to this agent, and very recently these responses have been correlated with the presence of activating mutations in the tyrosine kinase domain of EGFR. EGF interacts with EGFR, leading to receptor dimerization, activation of its kinase activity and autophosphorylation of EGFR on tyrosine residues. EGF is also associated with the growth and invasion of various malignant tumors via different pathways. Several studies have shown that EGF is frequently elevated in lung cancer, and up-regulation of EGF has been shown to be related to disease progression and poor prognosis (Gorgoulis et al., 1992, Anticancer Res, 12, 1183-1187). This suggests that EGF plays a major role in lung tumorigenesis. Therefore, the EGF/EGFR interaction may be important for the development of lung cancer.
Herbal therapies have increasingly been considered viable alternative treatments for cancers. Lingzhi (a species of Basidiomycetes) is an herbal mushroom, used in traditional Chinese medicine for at least 2,000 years. Many therapeutic effects have been reported of Lingzhi species, such as immunomodulatory, anti-tumor, hepato-protective, antioxidant, and cholesterol-lowering effects (Jinn et al., 2006, Biosci Biotechnol Biochem, 70, 2627-2634). All of these therapeutic effects are attributed to triterpenoids, polyssacharides, and glycoproteins (Boh et al., 2007, Biotechnol Annu Rev, 13, 265-301; Jinn et al., 2006, Biosci Biotechnol Biochem, 70, 2627-2634). A new glycoprotein class in Lingzhi named fungal immunomodulatory proteins (FIPs) was recently identified. So far, at least 4 FIPs have been isolated and purified from Ganoderma lucidum, LZ-8, (G. lucidum), including FIP-fve (Flammulina veltipes), FIP-vvo (Volvariella volvacea), FIP-gts (Ganoderma tsugae), and FIP-gja (Ganoderma sinensis) (Hsu et al., 1997, Biochem J, 323 (Pt 2), 557-565; Ko et al., 1995, Eur J Biochem, 228, 244-249; Xuanwei et al., 2008, Planta Med, 74, 197-200). According to a previous study, FIP-gts from G. tsugae, a popular chemopreventive mushroom in Asia, has anti-cancer function and is involved in the regulation of hTERT/telomerase expression (Liao et al., 2006, Mol Carcinog, 45, 220-229). In addition, FIP-gts inhibits the growth of A549 cancer cells, leading to cell cycle arrest, consequently inducing premature cellular senescence in lung cancer cells. Moreover, FIP-gts results in significant inhibition of tumor growth in athymic nude mice implanted with A549 cells (Liao et al., 2008, Food Chem Toxicol, 46, 1851-1859). US 20100009915 provides a method for suppressing proliferation of a cancer cell and a method for suppressing a tumor cell mobility, comprising providing to the tumor cell a purified polypeptide of a fungal immunomodulatory protein, LZ-8.
U.S. Pat. No. 7,601,808 discloses an immunomodulatory protein (GMI) cloned from Ganoderma microsporum and this protein has immunomodulator efficiency. However, since GMI is a newly found immunomodulatory protein and its anti-cancer effects have not been investigated, there is still a need in the art to investigate its anticancer applications.